1. Field of the Invention
The subject invention relates to magnetic and other tape recording and reproducing methods and apparatus and, more specifically, to magnetic and other information carrier tape transport methods and equipment.
2. Description of the Prior Art
Broadly speaking, the magnetic tape transport art may be devided into the three categories concerned with "open loop", "closed loop" and "zero loop" equipment. In open loop equipment, the tape proceeds from a supply reel to a transducing head, thence to a capstan and pinch roller, and further to a takeup reel. This arrangement subjects the magnetic tape to vibrations and tension fluctuations originating at the supply reel. In an effort to overcome this disadvantage, the closed loop system employs the tape drive capstan and a tape turnabout roller or tape guide to provide a tape loop which is mechanically isolated from the tape supply for an improved recording and playback of information relative to the tape. Despite these improvements, the closed loop design is still subject to performance degradation through tape vibration in the loop.
Accordingly, the tape transport art concerned with instrumentation tape recording and other high precision endeavors, has been moving in the direction of zero loop equipment in which the information transducing operation takes place at the tape drive capstan itself. Initially, the information transducing devices were placed directly into contact with the tape on the capstan. A drawback of this extreme zero loop design is that even slight tape eccentricities cause serious head to tape separation and head wear problems. These and other performance degradations practically exclude the extreme zero loop design from most practical applications.
In an effort to avoid the disadvantages of the zero loop design while at the same time retaining as much as possible of its advantages, there have been proposals and designs according to which the tape has been lifted off from the capstan in order to provide for a performance of information transducing operations closely to the capstan but nevertheless out of direct contact therewith. One design of this kind has used a pneumatic capstan or adjacent pneumatic device for forming a bulge in the tape at the capstan and for pressing such bulge against transducing head equipment. In practice, such a design encumbers the transport with pneumatic equipment and considerably reduces the attainable traction the capstan is capable of exerting on the tape. These problems are compounded if more than one read-write head assembly is needed in the operation of the equipment.
Another tape of proposal has employed a curved tape guide with a radius of the same order of magnitude as the radius of the capstan for a separation of the tape from the capstan for the performance of information transducing functions. This design also places severe limitations on the attainable tape drive traction and tends to require the use of floating or movable tape supply and takeup rolls.
In order to enable the type of interlace track operation prevailing in the instrumentation tape recorder field and requiring a spacing of 11/2 inches between corresponding heads, it has been proposed to lift the tape off the capstan at two spaced locations with the aid of rollers, posts or airbearings providing each two unsupported tape portions at which the recording and playback operations are effected. Lifting the tape off the capstan periphery at two locations severely reduced the total capstan-to-tape traction area for a given diameter. Accordingly, proposals of the latter type are typically characterized by very large capstan diameters, making for a high-inertia tape drive. In practice, even such a sacrifice was insufficient and complex vacuum-action capstans and associated vacuum equipment had to be employed to provide workable tape transports in high-quality type of environments.
A reduction is requisite capstan diameter eventually resulted when two of four recording heads were placed at the tape input of the capstan, while the remaining two heads were located at the tape turnabout side, where a circular cylindrical roller effected the tape turnabout. In practice, use of a circular cylindrical turnabout roller, however, necessarily spaced the tape away from the capstan by a distance larger than the diameter of the turnabout roller, which significantly reduced the useful capstan-to-tape traction area, necessitating again an increase in the capstan diameter to provide enough tape-to-capstan contact periphery. Moreover, the practical manifestation of the latter proposal was incapable of preserving the tape loop when the heads were removed from their operating positions. In consequence, and in order to have sufficient effective traction surface in all operational modes of the tape transport, it was necessary with that proposal to keep the heads in engagement with the tape during fast forward and rapid rewind of the tape. This more rapidly degraded the tape as well as the head surfaces through excessive wear.
Accordingly, there have been proposals to revert to the absolute zero loop design in which the recording and playback heads bear directly against the tape on the capstan. In order to alleviate the damaging influences of capstan eccentricities and similar factors, a very thick elastomer sleeve has been placed on the capstan proper. This, is turn, has made the capstan subject to hygroscopic diameter variations and warping. Nevertheless, thick elastomer coatings on zero loop type capstans had been continued to be employed, even in designs wherein the tape is lifted off the capstan for the above mentioned purposes.